The present inventions are related to detection of data in a communication system, and more particularly to detection of a sector address mark from a channel.
A read channel integrated circuit is a component of a magnetic storage device. In operation, a read channel component converts and encodes data to enable a read/write head assembly to write data to a disk and to subsequently read data back. In, for example, a hard disk drive, the disk typically includes many tracks containing encoded data that extend around the disk in a radial pattern. Each track includes one or more of user data regions as well as intervening servo data regions. The information of the servo data regions is used to position the read/write head assembly in relation to the disks so that the information stored in the user data regions may be retrieved accurately.
FIG. 1 shows a storage medium 100 with two exemplary tracks 150,155 indicated as dashed lines. The tracks are segregated by servo data written within wedges 160, 165. These wedges include data and supporting bit patterns 110 that are used for control and synchronization of the read/write head assembly over a desired location on storage medium 100. In particular, these wedges generally include a preamble pattern 152 followed by a sector address mark 154 (SAM). Sector address mark 154 is followed by a Gray code 156, and Gray code 156 is followed by burst information 158. It should be noted that while two tracks and two wedges are shown, hundreds of each would typically be included on a given storage medium. Further, it should be noted that a servo data set may have two or more fields of burst information.
A servo search mode is typically included in existing magnetic recording systems that allows for detecting a servo data pattern embedded between user data regions of a storage medium. Once the servo search mode identifies a servo data pattern, a normal processing mode begins where the preamble is detected and a sampling clock is recovered based on the frequency and phase of the detected preamble. Using the recovered sampling clock, the subsequent servo address mark is detected, and a location thereof identified. The following Gray code data and burst demodulation information is processed based on a predicted distance from the location of the sector address mark.
In some cases, a pattern similar to the servo preamble is detected in the user data region and mistaken for the servo preamble. In such cases, the system may be improperly switched to normal mode where the succeeding data stream is continuously queried for the expected sector address mark. Where a servo preamble is errantly identified in user data region, the normal mode operation will either timeout because of an inability to identify a subsequent sector address mark, or worse, a pattern matching the sector address mark will be found causing the subsequent data to be improperly processed as Gray code and burst information fields. Among other things, this can result in problematic positioning errors of a read/write head assembly in relation to the storage medium.
Hence, for at least the aforementioned reasons, there exists a need in the art for advanced systems and methods for detecting and processing servo data.